A typical apparatus for reading and writing information through sequential access, such as a magnetic tape recording and playback apparatus, reads and writes information for every track and therefore requires highly precise tracking (track following function) during recording and playback of information. In playback mode, the range of the track width corresponds to the scanning area of a playback head.
Such high-precision tracking is also required during overwriting (writing new information to an already-written tape), and a portion changed by overwriting is also processed for every track.
A high density is achieved by narrowing the minimum writing unit (track width); a narrowed track width, however, often prevents successful tracking.
In response to recent demands for recording media with increased storage capacity, the effective track width is narrower than the width of the scanning area of the playback head, inevitably causing the width of the scanning area of the playback head to span two contiguous tracks in some cases.
Unfortunately, a conventional information recording and playback apparatus often generates an error during playback due to a narrowed track width if the width of the scanning area of the playback head spans two contiguous tracks, especially if one of the two contiguous tracks is an already-written track and the other is a newly written track.
The mechanism of the generation of the error described above is as follows: narrow-width tracks cause a track in a newly written portion to shift with respect to the original track or causes the frequency of recorded tracks to differ between the newly written portion and the original portion due to differences in the recording system during recording, leading to poor frequency-locking of a phase locked loop (PLL) used in the playback system and finally to loss of synchronization. In short, such an error results from mixing of old original data and newly written data or a malfunction of the PLL.
In order to solve these shortcomings associated with the conventional information recording and playback apparatus, an object of the present invention is to provide an information recording and playback apparatus for preventing the generation of a playback error in a portion of narrow-width tracks having information overwritten thereon.